36 SCIENCE PROGRESS 



Cole expands an illuminating suggestion of Liesegang's, that the 

 layers of flint in chalk are due to rhythmic precipitation of 

 silica from a solution moving uniformly through the rock in a 

 direction perpendicular to the bedding planes. 



Abbott describes tubular concretions of ferriferous, calcare- 

 ous, and siliceous composition which occur in various sedi- 

 mentary rocks. For their origin he suggests osmotic growth 

 in colloids similar to the growths produced by Leduc in certain 

 solutions. Liesegang, however, has applied his theory of 

 rhythmic precipitation to these structures, and probably only 

 ihe test of experiment will decide between the rival views. 



Economic Geology 



HEINECKE, L., Road Material Surveys in 1914, Geol. Survey of Canada, Memoir 85, 

 1916, pp. 244. This gives an excellent summary of the various kinds of roads, 

 road-making materials, and tests for the road-making qualities of stone. 



Spencer, A. C, The Atlantic Gold District and the North Laramie Mountains, 

 Wyoming, United States Geological Survey, Bull. 626, 1916, pp. 85. 



Graton, L. C, and McLaughlin, D. H., Ore Deposition and Enrichment at 

 Engels, California, Econ. Geol. 1917, 12, 1-38. 



Umpleby, J. C, Genesis of the Success Zinc-Lead Deposit, Cceur d'Alene 

 District, Idaho, ibid. 138-53. 



Graham, R. P. D., Origin of Massive Serpentine and Chrysotile-Asbestos, Black 

 Lake-Thetford Area, Quebec, ibid. 1 54-202. 



MINERALOGY AND CRYSTALLOGRAPHY. By Alexander 

 Scott, M.A., D.Sc, University, Glasgow. 



Synthetic Mineralogy. — The workers of the Geophysical Labora- 

 tory continue to advance our knowledge of this branch of the 

 subject in several valuable papers. Bowen (Amer. Jour. Set. 

 43, 115, 1917) has made a thermal investigation of the sodium- 

 potassium nephelites. The sodium salt — NaAlSiO* — exists in 

 two enantiotropic forms, nephelite and carnegieite, with a- 

 transformation point at i248°C. The form of the potash 

 salt which is stable below 1 540 C. is kaliophilite, which is 

 isomorphous with sodium-nephelite, but above that tempera- 

 ture an orthorhombic modification is formed. The latter forms 

 a eutectiferous series with carnegieite, but the low-temperature 

 modifications give a continuous series of solid solutions. The 

 composition of natural nephelite is to be explained by the 

 presence of albite and anorthite molecules in solid solution in 

 the alkaline nephelites. 



Johnston, Williamson, and Merwin {Amer. Jour. Sci. 41, 



